1. Technical Field
The present invention relates to a light-emitting device, a method for manufacturing the same, and an electronic apparatus.
2. Related Art
Light-emitting devices (full-color display devices) for displaying a color image on a screen, the light-emitting devices including a plurality of pixels that constitute a screen, each of the pixels including a plurality of subpixels, each of the subpixels including an electroluminescent (EL) element, such as an organic EL element or an inorganic EL element, have been developed. Examples of such light-emitting devices include RGB light-emitting devices, in which each of the pixels includes red, green, and blue subpixels, and RGBW light-emitting devices, in which each of the pixels includes red, green, blue, and white subpixels.
Examples of the RGB light-emitting devices include: a first device, in which a light-emitting layer of each of the subpixels is formed of an EL material that emits colored light corresponding to the subpixel; a second device, as disclosed in JP-A-2001-57290, in which light-emitting layers of the subpixels are formed of an EL material that emits white light, and each of the subpixels includes a color filter with the characteristic corresponding to the color of the subpixel; and a third device, in which light-emitting layers of the subpixels are formed of an EL material that emits blue light, and each of the red and green subpixels includes a color-conversion layer with the characteristic corresponding to the color of the subpixel.
An example of the RGBW light-emitting device is a fourth device, in which light-emitting layers of the subpixels are formed of an EL material that emits white light, and each of the red, green, and blue subpixels includes a color filter with the characteristic corresponding to the color of the subpixel. The fourth device has a white subpixel in addition to the configuration of the second device. When a pixel displays white, the light emitted from the light-emitting layer of the white subpixel is used.
The first device requires the use of a polarizing plate for preventing reflection of external light, thereby having low utilization efficiency of emitted light. The second device loses a significant portion of the emitted light because of the presence of the color filters, thereby having low utilization efficiency of emitted light. The third device requires the use of the color filters to block entrance of unwanted light, and loses a portion of the emitted light because of the presence of the color-conversion layers and the color filters, thereby having low utilization efficiency of emitted light. Accordingly, the first to third devices have low utilization efficiency of emitted light. In order to realize sufficiently high display quality, the first to third devices have to consume a large amount of power.
The fourth device has a sufficiently high utilization efficiency of emitted light, because, when a pixel displays white, light emitted from the white subpixel is output unobstructed. However, when a pixel displays red, green, or blue, the utilization efficiency of emitted light in the fourth device is reduced to the same level as the second device. Because red and blue are less easily perceived in human vision than green, a pixel consumes more power to display red or blue than green. To reduce power consumption, it is important to improve the utilization efficiency of emitted light when a pixel displays red or blue. As described above, however, the utilization efficiency of emitted light when a pixel displays red or blue is as low as 30% or 10% in the fourth device. In order to realize sufficiently high display quality, the fourth device also has to consume a large amount of power.
Now, let us consider a fifth device, which is a modification of the fourth device. In the fifth device, a light-emitting layer of each of the subpixels is formed of an EL material that emits colored light corresponding to the subpixel. Because the utilization efficiency of emitted light in each of the subpixels is sufficiently high in the fifth device, the power consumption can be reduced. However, four types of EL materials need to be used in the manufacturing process. It is clear that the manufacturing process of the fifth device is extremely complex compared with that of the first device, which requires the use of three types of EL materials.